Thermally responsive spatially programmable soft actuators with multiple response states enabled by Grayscale UV light processing.

Soft actuators hold great promise for applications in biomimetic robots, artificial muscles, and drug delivery systems due to their adaptability in diverse environments. A critical aspect of designing thermally responsive soft actuators is to achieve spatially programmable actuation under a global thermal stimulus. Different local actuation behaviors can be encoded in one actuator to enable complex morphing structures for different tasks. However, it is challenging to achieve programmability beyond one or binary states. This work introduces a new grayscale ultraviolet (UV) light processing method to fabricate soft actuators with spatially tunable Young's modulus, enabling multiple programmable states in one actuator. Together with a liquid crystal elastomer actuation layer and a photothermal heating layer, the LCE programming layer with spatially programmable moduli allows different regions of the soft actuator to bend to controllable extents under a global thermal stimulus. Various shape morphing patterns can be encoded using UV photomasks with spatially controlled grayscales. Additionally, caterpillar-inspired robots capable of bi-directional crawling and octopus-arm-inspired structures for object manipulation are demonstrated. This work represents advancements in the programmability of thermally responsive soft actuators, laying the foundation for their applications in advanced soft robotic systems.